When Michigan’s oldest operating nuclear power plant shut down in 2022, it was supposed to be for good. The plant, which sits on the coast of Lake Michigan, had company — dozens of other reactors had already been wound down.

But soon after the turbines stopped spinning, those plans changed. A little-known company from Camden, N.J., quietly started taking steps to attempt what no one had done before in the United States: restart a shuttered nuclear reactor. The process would take about two years, estimated the company, Holtec International.

Four years later, the plant, called Palisades, is not yet generating power.

The delay is a reminder of the challenges of expanding nuclear energy, even at a time when the technology enjoys broad bipartisan support. The United States has built just two new reactors in the past decade. They cost more than twice as much as planned and arrived seven years late, quelling interest across the energy industry and on Wall Street.

Some of the setbacks at Palisades were expensive and time consuming, including discovering extensive corrosion of the equipment that uses hot radioactive water to produce high-pressure steam. Others were mundane: supply chain headaches, an underground water line that leaked, valves that needed replacing.

None of these challenges were unforeseeable. Holtec had never operated a nuclear power plant. It also embarked on the project almost as soon as it bought Palisades. The company applied for federal subsidies for the effort seven days after the sale closed, according to records obtained by The New York Times.

By the time Holtec decided to restart Palisades, it had not completed a top-to-bottom inspection of the plant, Jeff Borah, the general manager of plant operations, said in an interview.

“We didn’t take the time to really plan out the whole project before we started doing work,” Mr. Borah said. “It’s like building a fire truck on your way to the fire.”

Now, Holtec is aiming to load fuel into the nuclear reactor in September, records show, and generate power by the end of the year. It faces a March 2027 contractual deadline.

The Palisades restart is part of a larger effort to revive nuclear energy in the United States. The Trump administration, like the Biden administration before it, is dangling billions in federal financing to kick-start investment. In June, the Energy Department offered up to $17.5 billion in subsidized loans for the purchase of nuclear equipment in hopes of having 10 large reactors under construction by 2030.

“We’re going to do whatever it takes to get that ball rolling,” Chris Wright, the energy secretary, said in an interview.

Jigar Shah, who ran the Energy Department’s loan office during the Biden administration, said Holtec’s work encouraged other companies to pursue similar projects. Constellation Energy and NextEra Energy followed Holtec by agreeing to reopen nuclear reactors in Pennsylvania and Iowa.

“I don’t think there’s anything wrong with Holtec being optimistic,” said Mr. Shah, whose office backstopped a low-interest loan of up to $1.52 billion to finance restarting Palisades, which has the capacity to meet the electricity needs of more than 800,000 homes. “They thought that they were going to inherit a plant that was in much better shape. ”

A Holtec executive and former nuclear regulators said it was not surprising that the company had decided to reopen Palisades without having inspected certain equipment, particularly given that it had owned the facility for only a short time.

“There are some systems you can’t really inspect until you start the project,” said Rick Springman, Holtec’s president. As an example, he pointed to a turbine that needed to be disassembled before being thoroughly examined, a process that took months.

“The difference between building a new house and rehabbing an old house is there is going to be discovery,” Dr. Springman said.

Other projects have not been as fraught. Constellation Energy says it expects to restart the undamaged reactor at Three Mile Island in Pennsylvania next year, ahead of schedule. Unlike Holtec, Constellation owned and operated its plant for many years.

Palisades was bought from Entergy, a utility company. An Entergy spokesman praised Holtec’s restart effort but did not comment on the plant’s condition when it was sold.

The plan to revive Palisades, which opened in 1971, has put off some locals, including people who say they support nuclear power. Worries range from the amount of taxpayer money being spent and Holtec’s lack of expertise operating nuclear reactors to cancer risks. A recent study led by Harvard’s public health school found higher cancer mortality rates in counties near operating nuclear plants.

“It doesn’t seem like a smart idea to try to restart something that’s this old,” said Dave Simonelli, who spends summers less than a mile from Palisades as the crow flies. The 69-year-old described himself as being pronuclear, but concerned with safety: “Why restart an antique? A car in the junkyard.”

Palisades was built at the vanguard of a booming business in the United States. By the end of the 1970s, the country had more than 60 reactors. And by the mid-1990s, that figure had topped 100.

But people soured on nuclear power after a reactor at Three Mile Island partially melted down in 1979 and the Chernobyl disaster in 1986. Companies canceled dozens of projects. One reactor after another shuttered as they struggled to compete with power plants that burned natural gas, which was becoming cheaper.

By 2022, however, public attitudes toward nuclear power were improving, including among Democrats who had been skeptical of the technology. Nuclear reactors can generate electricity around the clock without releasing greenhouse gases.

Officials working in the Biden administration and for Michigan’s Democratic governor, Gretchen Whitmer, tried unsuccessfully to convince Entergy to keep Palisades open. So they turned to Holtec.

It was a gamble. The company was in the business of making the equipment to store spent nuclear fuel and dismantling old reactors, not running plants.

Holtec quickly estimated that reopening Palisades would take two years and cost more than $1.9 billion, including a contingency for cost overruns, records show.

It took almost that long just to line up customers and other financing after the Energy Department rejected Holtec’s initial application for subsidies. Holtec eventually pushed the restart date to October 2025 and then to the end of this year.

Two electric cooperatives, Wolverine Power Cooperative and Hoosier Energy, agreed in 2023 to buy the power Palisades produced for 28 years at a fixed price. A Times review of a Holtec securities filing indicates the co-ops may have agreed to pay roughly $59 per megawatt-hour. That is slightly higher than the market rate for wholesale electricity in the region.

Holtec and Wolverine Power declined to comment on the price. Hoosier Energy did not respond to requests for comment.

It didn’t hurt that the government was showering Palisades with money, including $300 million from Michigan and the promise of federal tax credits once the plant was running. Separately, the Agriculture Department awarded $1.3 billion to Wolverine and Hoosier in late 2024, most of it to be put toward this effort.

It was around then that Holtec discovered a major problem. The plant’s twin steam generators, among its most expensive equipment, were more degraded than the company had expected.

Holtec plugged or repaired thousands of skinny U-shaped metal tubes inside the generators. “That was a significant delay in the project, months,” said Mr. Borah, the operations manager.

The Nuclear Regulatory Commission signed off on Holtec’s approach, which activists and some residents worry was insufficient.

“Here at Palisades, there have been so many compromises,” Michael J. Keegan, a co-chairman of the environmental group Don’t Waste Michigan, testified at a June N.R.C. hearing where he argued that Holtec should have replaced the steam generators.

Dr. Springman, Holtec’s president, said the repaired equipment had been extensively inspected and tested. “We feel very comfortable with the safety of the component,” he said.

This spring, Palisades resembled a Lego set that was being reassembled. Scaffolding draped in orange fabric straddled the turbines and a generator that converts steam into electricity. Nearby, a worker cleaned pipes. A screen showed men clad in white protective suits inspecting a giant metal barrel designed to hold nuclear fuel in the nearby reactor building.

Holtec, which is responsible for any additional expenses tied to the project’s delay, declined to share an updated cost estimate.

Mr. Springman said that describing the project as delayed was “unfair” since the contractual deadline for restarting the facility is March 2027.

It is a sensitive time for Holtec, which this month filed paperwork for an initial public offering. Armed with its experience at Palisades, the company wants to build and operate smaller nuclear reactors, starting at the Michigan site.

It is riding growing enthusiasm for nuclear power. The federal government, technology companies and others are offering to invest in or lend money to nuclear companies. Elsewhere, the energy crisis stemming from the war with Iran is pushing countries toward nuclear energy.

That Palisades has been slow to reopen was of little concern to Gail Patterson-Gladney, a commissioner in Van Buren County, the plant’s home. “We are like a prototype, something that’s never been done,” Ms. Patterson-Gladney said.

Jim Wilson, 66, who lives down the road from Palisades, has been readjusting to the idea of having the plant back online. He recently bought a Geiger counter to measure background radiation levels in his home.

“I have faith that they’ll do it right,” Mr. Wilson said. “Otherwise I’d have a for-sale sign on my house.”